Commonly assigned U.S. Pat. No. 4,893,307, issued Jan. 9, 1990, "Method and Apparatus for Linking SNA Terminals to an SNA Host Over a Packet Switched Communications Network", D. B. McKay, R. M. Morten and M. P. Marsili, describes an architectural model of the Department of Defense (DoD) protocol suite.
Referring to FIG. 1, the architecture is said to be similar to, but not identical with, the International Standards Organization (ISO) Open Systems Interconnection (OSI) architecture.
A Defense Data Network (DDN) standard establishes criteria for an Internet Protocol (IP) which supports the interconnection of communication LANs.
It introduces the Internet Protocol's role and purpose, defines the services provided to users, and specifies the mechanisms needed to support those services. The standard also defines the services required of the lower protocol layer, describes the upper and lower interfaces, and outlines the execution environment services need for implementation.
A Transmission Control Protocol (TCP) is a transport protocol providing connection-oriented, end-to-end reliable data transmission in packet-switched computer LANs and internetworks.
The Internet Protocol (IP) and the Transmission Control Protocol (TCP) are mandatory for use in all DoD packet switching networks which connect or have the potential for utilizing connectivity across network or subnetwork boundaries. Network elements, such as hosts, front-ends, gateways, etc., within such networks which are to be used for internetting must implement TCP/IP.
The Internet Protocol is designed to interconnect packet-switched communication LANs to form an internetwork. The IP transmits blocks of data, called internet datagrams, from sources to destinations throughout the internet. Sources and destinations are hosts located on either the same subnetwork or on connected LANs. The IP is intentionally limited in scope to provide the basic functions necessary to deliver a block of data. Each internet datagram is an independent entity unrelated to any other internet datagrams. The IP does not create connections or logical circuits and has no mechanisms to promote data reliability, flow control, sequencing, or other services commonly found in virtual circuit protocols.
The DDN standard specifies a host IP. As defined in the DoD architectural model, the Internet Protocol resides in the internetwork layer. Thus, the IP provides services to transport layer protocols and relies on the services of the lower network protocol. In each gateway, a system interconnecting two or more LANs, an IP resides above two or more LAN's protocol entities. Gateways implement IP to forward datagrams between LANS. Gateways also implement a routing protocol to coordinate signalling and other internet control information.
Various Network Access Protocols reside below the IP and may include, by example, an Ethernet protocol, an X.25 protocol, and, of particular interest herein, a wireless network protocol.
The Internet protocols were originally developed with an assumption that users, each of which is assigned a unique Internet address, would be connected to the network at fixed locations. However, for portable and handheld computers employing a wireless protocol the movement, or migration, of users about the network is typically the rule rather than the exception. As a result, a problem is created in that the implicit design assumptions of the Internet protocol are violated by this type of usage.
The problem that arises thus relates to providing optimal network layer routing with a mobile host, when network layer address(es) assigned to a host may not bear any network topological significance. The problem arises because of a requirement for a host to have an identifier that remains fixed, even as the host moves, while at the same time providing sufficient information in the network layer to make network layer routing feasible.
It is thus an object of this invention to provide a method for optimizing network layer routing between a pair of hosts, where at least one of the hosts is mobile and, as a result, does not have a fixed connection location with respect to the network.
It is another object of the invention to provide a method for optimizing network layer routing between a pair of hosts, where at least one of the hosts is mobile, in the context of a network that operates in accordance with the Internet or an Internet-type protocol.